Current charge plate fabrication techniques are limited in the number of lines and spaces that can fit in a linear dimension. For example, current charge plates are typically made with 300-lines per inch resolution. Although higher resolutions can be achieved with these techniques, the higher resolutions come at great cost for development and eventual product yield is slower. A need has existed for a charge plate with a high resolution that can be made inexpensively.
Thin film structures for charge plates have the advantage of extremely high resolution (smaller line widths and spaces) and high yields. The disadvantage of fabricating a charge plate from a thin film processes is that the thin film technique has been unsuccessful in providing an electrode structure that extends to the edge and over the charging face of the charge plate.
The main difficulty in defining electrodes that continue from a top surface to an edge surface lies in the difficulty of photo imaging the pattern. Typically, spun liquid photoresist tends to “ball up” along an edge giving rise to thicker cross-sectional area. Since the amount of photo energy needed to expose properly the photoresist layer is dependent on the thickness of the photoresist layer, the balling up causes unacceptable results because consistency cannot be assured.
Another difficulty with thin film processes arises is attempting to expose a second surface after a first surface has already been exposed. Exposing the second surface has traditionally caused a detriment to the previously exposed material.
Other thin film techniques exist to from electrodes that “go around the edge.” For example, a shadow mask can be constructed out of wire or out of an L-shaped part with grooves and touch one side and edge to be patterned. After the shadow mask is constructed, sputtering or evaporation of the remaining side can be patterned and etched.
Accordingly, a need exists for a technique that creates extremely high resolution (smaller line widths and spaces) and high product yields in a cost effective manner.
The present embodiments described herein were designed to meet these needs.